Field of the Invention
This invention relates to a passive radar ranging system and method, that is, using only the threat radar's signal to calculate the range of the threat, and more particularly relates to a passive doppler differential ranging system and method.
Description of the Prior Art
Conventional radar systems employ various methods to calculate the range of a threat radar passively. One such method is commonly referred to as a triangulation ranging technique.
Triangulation ranging is shown in FIG. 1. Two separate receivers, R1 and R2, situated at two remote locations, X and Y, respectively, detect the target at different azimuth angles, .THETA.1 and .THETA.2. The radar system would take the azimuth information obtained from the two receivers and the distance d between the two receiver locations and would triangulate their intersection to resolve the target's range.
Triangulation techniques may be applied in airborne ranging radars. For example, two airplanes may be used, each carrying one of the radar receivers, R1 and R2. If the spacing between the two radars is determined accurately, i.e., to calculate the distance d, and the azimuth angles, .THETA..sub.1 and .THETA..sub.2, of the threat from the two radar receivers are measured, then triangulation between the two airplanes and the threat radar will result in the range of the threat.
Triangulation techniques may also be employed with a single airplane by having two radar receivers mounted on the airplane a distance d apart from each other and knowing the azimuth angles .THETA..sub.1 and .THETA..sub.2 of the threat from the receivers.
It is evident from the above description that conventional triangulation ranging techniques require two separate azimuth angle measurements.